Laying a Limecrete Floor Part 1

This might be a bit detailed for some of you, but I have been researching the use of limecrete as a breathable kitchen floor for some time and have found very little good advice on t'internet; hence I thought that some detail in the public domain might be found useful.  I shall publish another entry soon detailing some other events of the week.

This week, at last, I bit the bullet and engaged Chris and Shane to dig out the existing floor and help me lay the limecrete slab.  The general deal was that they would do the physical bit and I would provide the technical know-how (aided by desperate telephone calls to Mike Wye).  Of course life is not like that and so I am now absolutely shattered (as indeed they are, and they are half my age!).

When we first saw the kitchen I immediately knew that we would have to sort the floor (photo right).  The red and black 6" quarry tiles, in a pleasing diagonal pattern, were damp and sadly neglected.  They were suffering from a variety of additional coverings (like rotted lino and bitumen), and many (mostly red ones) had lost their flat surface entirely, revealing a pitted face with a white bloom.  I tried various techniques of cleaning but nothing persuaded me (far less Jane!) that we would be able to live with the end result for the duration of our intended retirement.  Delaying this was not an option as there would be no real way of doing it once we had fitted the new kitchen and were living in the house.  Another issue was the strip of bare concrete (foreground on photo) which ran across the room where there used to be a wall; this pre-dated the tiles, as the diagonal lines on either side did not match! 

I made an early decision that what I wanted to do was to lay a breathable limecrete floor, and researched this on the internet.  It can be difficult to get Building Control approval for this material, but there is an exemption for listed buildings on account of the foundations usually being shallower than the required depth to meet Part L (Conservation of Fuel and Power).  I knew that the foundations were about 8 or 9 inches below the floor level, and the essential detail here is to dig down at 45 degrees from the walls at a point a small way above the bottom of the foundations so that the integrity of the walls  is not affected.  If you are cautious like me then that small way is about 6 inches.

I got the team at Mike Wye to do the materials quotation which also gave me the essential design of the floor.  It seemed to me that the quantities required were enormous (4 tons in photo left) so I asked them to do it again; the result was the same so I just had to trust their figures.  Of course, they were very accurate - see later. Their design uses LECA (lightweight expanded clay aggregate) which comes in various sizes but essentially looks like an unappetizing version of Maltesers without any chocolate.  A coated version of LECA is used as a loose lay foundation; this allows the floor to breathe but does not allow any water to rise by capilliary action.  On top of this the main slab is made of a slightly smaller LECA, uncoated (presumably to allow better binding), mixed with NHL5 (Natural Hydraulic Lime).  A breathable membrane is used both below and above the loose lay LECA to prevent migration between the layers.  On top of the slab a screed of NHL5 and sharp sand is laid, on which the chosen floor surface is laid.  Most of the insulation is from the loose lay so I chose to use 200mm of this, with a 100mm slab on top.  This was the task for the week, as we will let it go off before laying the screed and flagstones.

The first task was to remove all the tiles - only about 900 of them - and then Chris and Shane removed (in about three minutes) the old (1950s) fireplace - see result in photo left.  What I had not really bargained on was how much spoil there would be (photo right), and the sheer physical effort in getting it out of the house. Everything had to be lifted up a couple of feet  - well, we were digging down - and extracted through the fairly narrow single French door.

I estimate that they removed something like 10 tons of lime mortar and soil in three days, all by hand through that single doorway.  The end result was basically an empty swimming pool where there will soon be a kitchen.  I also removed about half a ton of rubble which filled the old fireplace - compare the photo left (after excavation, with membrane laid) with the one above.  I was expecting to build a rectangular alcove for the new woodburning stove, and it was there all the time! 

So we worked along from the far end, laying the loose lay LECA with the membrane over it up to a bit of temporary shuttering, then the slab mixture on top up to a couple of feet back.  Then we added LECA in front of the shuttering, removed the shuttering, unrolled the membrane and added more slab mixture, and so moved on.  The addition of the LECA in front of the shuttering is key as otherwise the edge would move significantly when the shuttering is removed and this might allow the slab mixture to drop down a bit.  Here's Chris (right) doing a bit of levelling with some marker stakes for the next bit of shuttering.

 
Finally, we had a floor slab.  I know it doesn't look much for the result of so much work, but I'm convinced that it's a good way of controlling dampness in such an old building.

We actually received 84 bags of the loose lay LECA, and 42 of the stuff to mix with the mortar; we used 81 and 38 respectively - a surplus is far preferable to running out.  The LECA totalled about three tons, and we also used almost exactly half a ton of NHL5.  All that remained was to clear up, including removing the remaining mortar (for the screed next week) from the lawn to the house.  I have to confess that I was surprised to see the entire lawn cleared in just seven hours, and I bet the neighbours were as well, considering that half of the lawn is theirs!